Coherent control of single spins in silicon carbide at room temperature (1407.0180v2)

Abstract: Spins in solids are cornerstone elements of quantum spintronics. Leading contenders such as defects in diamond, or individual phosphorous dopants in silicon have shown spectacular progress but either miss established nanotechnology or an efficient spin-photon interface. Silicon carbide (SiC) combines the strength of both systems: It has a large bandgap with deep defects and benefits from mature fabrication techniques. Here we report the characterization of photoluminescence and optical spin polarization from single silicon vacancies in SiC, and demonstrate that single spins can be addressed at room temperature. We show coherent control of a single defect spin and find long spin coherence time under ambient conditions. Our study provides evidence that SiC is a promising system for atomic-scale spintronics and quantum technology.

• The paper demonstrates room temperature coherent control and optical detection of single spin defects in 4H-SiC.
• The paper employs electron irradiation and solid immersion lenses to achieve spin coherence times of up to 500 µs with potential extension to 1 ms.
• The paper identifies a metastable state essential for spin polarization, a key step towards scalable quantum computing applications.

Coherent Control of Single Spins in Silicon Carbide at Room Temperature

The paper undertaken by Widmann et al. explores the potential of silicon carbide (SiC) as a host for single spin qubits at room temperature, focusing on silicon vacancies (V2 centers) within the 4H-SiC polytype. This work addresses a crucial challenge in the field of quantum spintronics: isolating and manipulating single spin defects in a widely manageable solid-state environment, which could have substantial implications for quantum computing and information processing.

The primary achievement of the paper is the demonstration of coherent control and optical detection of a single spin in silicon carbide at ambient conditions. Through electron irradiation techniques applied to high-purity SiC wafers, the team managed to create V2 centers at a density suitable for isolating single defects. The use of solid immersion lenses (SILs) facilitated enhanced collection of fluorescence emission from these single centers, overcoming the challenge of weak spin signals.

Key Findings

1. Optical and Spin Properties of SiC: The paper revealed the photoluminescence properties of silicon vacancies in SiC by examining their zero-phonon lines and demonstrating a stable optical spin signal without significant blinking—a common issue in such setups. This stability was observed even under continuous laser illumination, indicating robustness for potential practical applications.
2. Spin Coherence and Manipulation: The research highlights the capability of room temperature coherent spin control, confirmed through optically detected magnetic resonance (ODMR) experiments. The spin coherence time in the V2 centers was found to extend to 500 µs, and potentially up to 1 ms, under certain conditions. This offers a promising coherence time scale for practical quantum computing requirements.
3. Metastable State Identification: Through detailed modeling and experimentation, it was suggested that a metastable state exists, which plays a critical role in spin polarization at room temperature. This identification forms the basis for a deeper understanding and further refinement of using SiC in spin-based applications.
4. Challenges and Enhancements: Despite the success, some challenges remain, primarily the weak spin signals from single defect centers. However, ensemble experiments at cryogenic temperatures show dramatically enhanced signals, suggesting that further technical advancements could mitigate this issue. The paper also suggests the potential for reducing defect and impurity concentrations through optimized growth conditions, which could further enhance spin coherence.

Implications and Future Directions

The implications of this research are significant for advancing quantum technologies. SiC's mature fabrication techniques make it an attractive alternative to other systems such as diamond or silicon-based spin qubits, due to its superior thermal and electrical properties alongside the capability to host stable quantum states.

Theoretical models predict that SiC could support other defect types exhibiting long coherence times, providing a versatile platform for diverse quantum applications. The integration of spintronics, electronics, and photonics into a single SiC-based system points toward scalable quantum devices, offering the possibility of widespread implementation with existing semiconductor technology.

Future developments could focus on refining the control and readout processes of SiC defect spins at room temperature. Suppressing electron spin bath interactions and enhancing signal detection through advanced materials engineering could pave the way for scalable quantum architectures. The ongoing research and improvements in SiC technology indicate promising prospects for its application in quantum information science and the broader semiconductor industry.